Modern communication units, such as many mobile phone hand sets for example, include integrated antennas to transmit and receive radio frequency (RF) signals. Antenna designers strive to make these integrated antennas smaller and smaller, while at the same time covering as many frequency bands as possible. The small size allows the integrated antennas to be used in different types of end-user devices, while the wide operating frequency allows a given end user device to be used for different communication standards.
Unfortunately, these integrated antennas are sensitive to external use cases (described below). This sensitivity to external use cases, combined with the fact that a given antenna can be used over multiple frequency bands, makes it difficult to accurately match the impedance of the antenna to the impedance of the RF circuitry in the transmitter. Illustrative external factors can include whether or not a hand is positioned on the phone (and the particular position of such a hand, if present), whether the phone is close to a user's head, and/or whether any metal objects are close to the antenna, among others. All of these external factors can alter the impedance of the antenna, thereby leading to impedance mismatch between the antenna and RF circuitry within the transmitter. Such impedance mismatch can degrade the power radiated by the phone and increase the phone's sensitivity to noise. From a user's perspective, impedance mismatch can ultimately lead to a reduction in talk time and/or a dropped call.
To provide better matching between RF circuitry in the transmitter and the antenna, handset designers use antenna tuners. Conventionally, handset designers have arranged sensors inside the phone's package to detect the presence or absence of the previously mentioned external factors. Then the detected environment is compared with known use cases (e.g., “free space”, “hand on the phone”, “close to head”, “metal plate” . . . ) and a corresponding predetermined tuner setting is chosen selected based on the detected use case.
Unfortunately, this conventional approach requires a large number of sensors inside the mobile phone, which increases the phone's volume and cost (particularly if there are a large number of possible use cases to be detected). For example, with regards to a “hand on the phone” use case, sensors may be needed to differentiate between “Man's hand . . . ”, “Woman's hand . . . ”, “Child's hand . . . ”, and to further differentiate each of these hand types as having “dry skin . . . ”, “normal skin”, “sweaty skin”, etc. Sensors might also be needed to detect a mobile phone's package and even its color, some of which can be changed via aftermarket accessories and which can affect impedance matching for the antenna. Further, because the tuner settings for each use case are dependant on frequency bands (and even frequency sub bands), the conventional approach requires a detailed analysis of use cases in a dynamic fashion for each new handset design. Having to analyze and store all of these use cases requires a large number of sensors, a significant amount of ROM, and processing power.
Therefore, although conventional antenna matching schemes are sufficient in some regards, they are less than ideal for several reasons. Accordingly, the inventors have devised improved antenna matching schemes as set forth herein.